What is the difference between RAM, ROM and secondary storage, and how do you choose a storage device?
Primary storage (RAM, ROM and virtual memory), the need for and types of secondary storage (magnetic, optical and solid state), and the factors used to choose a storage device.
An Eduqas GCSE Computer Science answer on primary storage (RAM, ROM and virtual memory), the need for secondary storage, the three types (magnetic, optical, solid state), and the factors used to choose a storage device.
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What this dot point is asking
Eduqas wants you to distinguish primary storage (RAM, ROM and virtual memory) from secondary storage, explain why a computer needs secondary storage, describe the three types of secondary storage, and choose a suitable device by weighing factors such as capacity, speed, portability, durability and cost. The comparison-style questions (RAM versus ROM, choosing a device) come up almost every year.
Primary storage: RAM, ROM and virtual memory
Why a computer needs secondary storage
RAM is volatile, so anything in it is lost when the power is off, and it is relatively small and expensive. Secondary storage solves both problems: it is non-volatile, so it keeps files when the computer is switched off, and it offers much greater capacity at a lower cost per gigabyte. This is where the operating system, applications, documents, photos and everything else lives between sessions.
The three types of secondary storage
Choosing a storage device
Try this
Q1. State whether RAM is volatile or non-volatile. [1 mark]
- Cue. Volatile (it loses its contents when the power is off).
Q2. Name the three types of secondary storage. [3 marks]
- Cue. Magnetic, optical and solid state.
Q3. State one reason a computer uses virtual memory. [1 mark]
- Cue. To run more programs than would fit in RAM, by using part of secondary storage as extra memory when RAM is full.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas Component 1, 20224 marksExplain two differences between RAM and ROM.Show worked answer →
Award up to two marks per difference, for the property and a correct statement of how RAM and ROM differ on it.
Volatility: RAM is volatile, so it loses its contents when the power is turned off; ROM is non-volatile, so it keeps its contents without power.
Read/write: RAM can be both read from and written to during normal use; ROM is read-only in normal use (its contents are fixed when made).
Purpose: RAM holds the programs and data currently in use; ROM holds the start-up instructions (the bootstrap or BIOS) needed to switch the computer on.
Markers reward a clear property plus a correct contrast. Just writing "RAM is faster" without the volatility or read/write point is not enough.
Eduqas Component 1, 20233 marksA photographer needs a portable device to store and transfer thousands of high-resolution images. Recommend a suitable type of secondary storage and justify your choice using two factors.Show worked answer →
Recommend solid-state storage (such as an SSD or a USB flash drive / memory card) (1 mark for a sensible, justified choice).
Justify with two factors (1 mark each), for example: it is portable and small, so it is easy to carry between locations; it has no moving parts, so it is robust and survives being moved or dropped; it has fast read/write speeds, so large image files transfer quickly; it has high capacity, so thousands of images fit.
Markers reward the factors being tied to the photographer's needs (portability, durability, speed, capacity), not generic statements. A magnetic hard disk could also be argued for capacity per cost, if justified.
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Sources & how we know this
- WJEC Eduqas GCSE Computer Science specification (from 2016) — Eduqas (2020)